The present invention relates to exothermic compositions comprising iron metals, neutral metal salts, water, and water holding agents, which generate heat by air oxidation of the iron metals, and more particularly to exothermic compositions which are excellent in heat elevation at the initial stage and are improved in handling.
Recently, exothermic compositions utilizing heat generated by air oxidation of iron metals have been widely sold as body warmers because they can be readily and safely handled without requiring fire. Known body warmers are produced by mixing iron metals, neutral metal salts, water, water holding agents, and the like, and packing the mixture in a bag, and then sealing the bag.
As the iron metals, there are employed granular iron and powdered iron having a large reaction area since these facilitate the oxidation reaction. Further, reduced iron powders prepared by a reduction method are popularly used.
Nevertheless, because the air oxidation of iron is essentially not vigorous, it takes about 3 or 4 hours to reach an equilibrium temperature (generaly 50.degree. to 60.degree. C.). Particularly in cold regions heat generation is inferior at the initial stage, and sometimes heat generation cannot be obtained.
As mentioned above, the exothermic compositions utilize heat generation by air oxidation of iron powders. In order to proceed with the reaction, water and chlorine ion or sulfate ion can be used. Amount of water is preferably such an amount that the sufaces of the iron powders are partially covered with water. When the amount of water is too small, water is consumed in a short time due to evaporation by the heat elevation, which results in termination of the main reaction. When the amount of water is too large, the surfaces of the iron powders are wholely covered with water reducing air-permeability, which prevents the iron from air-oxidation. For holding a suitable amount of water while maintaining a good air-permeability, there have been employed water holding agents such as powders of coconut husk, charcoal, wood, silica gel, vermiculite, pearlite, polyurethane foam, asbestos, water absorbing resin, and the like.
Since the water holding agents are, as mentioned above, used for holding water which is an essential component for the air-oxidation of iron, it is desired that the agents be lighter and cheaper and that the amount of the agents is as small as possible provided that the above condition can be obtained.
An object of the present invention is to provide exothermic compositions which are improved in heat elevation at the initial stage.
Another object of the present invention is to provide exothermic compositions which have an excellent water holding capacity and are improved in handling.